Differentials for automotive-type applications are used in many front or rear axles to transmit the power from the engine to the driven wheels of the vehicle. Conventional differentials permits a vehicle to turn corners with one wheel rolling faster than the other and generally include two side gears coupled to the output or driven shafts, which in turn are coupled to the respective left and right wheels of the vehicle. The differential case generally includes a ring gear driven by a pinion gear coupled to an end of the vehicle drive shaft driven by the engine. Side gears are located within and coupled to the differential case while typically being splined or otherwise coupled to the respective driven shafts. The side gears may be controlled by various means to permit the driven shafts to power both wheels during most vehicle maneuvers. But when turning, this arrangement of the differential permits the outer wheel to overrun (i.e., rotate faster than) the inner wheel, which lags (i.e., rotates slower). The amount of overrun rate is generally equivalent to the amount of lag.
There are a variety of differential types such as conventional or “open” differentials, limited slip differentials, and lockable or locking differentials. These types are distinguishable by how they handle various possible operating conditions.
Locking differentials contain mechanisms and features which cause the differential to prevent or limit rotational speed differences between the left and right driven wheels. Different methodologies are used to actuate these mechanisms. The most common means for actuation of the mechanism in a locking differential are pneumatic, hydraulic, electric, electromechanical, mechanical friction or some combination thereof.
Several conventional locking differentials are described in U.S. Pat. No. 5,413,015 (Zentmyer), U.S. Pat. No. 5,715,733 (Dissett) and U.S. Pat. No. 5,836,220 (Valente). Each of these conventional locking differentials attempts to provide a minimum amount of preload on a pair of driving clutch members such that the driving clutch members remain engaged with driven clutch members during low torque conditions (e.g., when the vehicle tires may be prone to easily rotate such as when the vehicle is on ice). For clarification herein, the terms “driving” and “driven” are intended to indicate separate clutch members. The driving clutch members are mechanically engaged to a drive shaft which is rotated by operation of an engine. The driving clutch members engage the driven clutch members through complimentary teeth. The driven clutch members, in turn, are respectively coupled to output shafts that drive the wheels of the vehicle.
Under low torque conditions, the minimum amount of preload establishing the engagement between the driving and driven clutch members is generated by a shear pin and spring assembly located in corresponding bores of the driving clutch members. Some embodiments may include a disk or spring cap positioned between the spring and the end surface of the shear pin while another embodiment employs concentric springs that engage the end surface of the shear pin. Nevertheless, the assembly process of inserting the shear pin and spring assemblies into the bores of the driving clutch members and establishing the minimum amount of preload has a number of drawbacks. By way of example, holding the shear pins and springs in the bores of one driving clutch member while attempting to engage the corresponding driving clutch member may result in one or more of the shear pins and/or springs falling out of its respective bore. In some cases a tool is used to move the shear pin and compress the spring, which then permits an E-clip or a C-clip to be placed over a groove in the shear pin and thus capture the shear pin in its bore. In other cases, the springs are inserted into openings formed in the driving clutch members.